Intercalary implant

ABSTRACT

An intercalary implant has two stem members and a collar. One stem member includes a stem portion to be received in the intramedullary canal of a native end portion of a long bone and a threaded male portion to be outside of the intramedullary canal. The second stem member also includes a stem portion to be received in the intramedullary canal of the opposite native end portion of the long bone. The second stem member has a spacer portion and a shoulder to be outside of the intramedullary canal. The collar has an annular base portion with an opening and a cylindrical female threaded portion. When assembled, collar connects the first and second stem members and the implant spans a gap in the shaft of the long bone. The parts can be assembled without distracting the native end bone portions in the proximal-distal direction to prevent damage to soft tissue around the native end bone portions.

CROSS-REFERENCE TO RELATED APPLICATIONS

This patent application is a divisional of U.S. patent application Ser.No. 10/403,357 filed Mar. 31, 2003, the disclosure of which is herebyincorporated by reference.

FIELD OF THE INVENTION

The present invention relates to prosthetic systems for replacement ofparts of bones, and more particularly to prosthetic systems forreplacement of mid-shaft parts of long bones.

BACKGROUND OF THE INVENTION

Severe trauma and disease can lead to significant amounts of bone loss.In some instances, it is necessary to excise intercalary bone from along bone, that is, part of the diaphysis or bone shaft between the endsof the long bone, but it is not necessary to excise the ends of the longbone. Thus, for example, a portion of the shaft of the humerus may needto be excised to remove a malignancy, while the ends of the humerusdefining parts of the shoulder and elbow joint may be healthy.Similarly, it may be necessary to excise part of the shaft of the tibiaor femur while the ends of these bones are healthy. Rather than removethe healthy ends of the bone, it may be desirable to leave the healthyportions of the bone in place and remove the damaged or diseased bone.In these circumstances, the empty span between the ends of the bone mustbe replaced with some type of mid-shaft prosthesis that spans thedistance between the native bone ends. The mid-shaft prosthesis caninclude stems that fit into the intramedullary canals of the native boneends and a body that extends between these stems. However, it may bedifficult to implant such a mid-shaft prosthesis. Implantation canrequire that the native bone ends be distracted proximally and distallyin order to fit the mid-shaft prosthesis into position. Since the nativebone ends are surrounded by and connected to soft tissue, distraction ofthe native bone ends can damage the soft tissue and the connectionsbetween the soft tissue and the native bone ends.

Moreover, different bones undergo different types of stress in use. Forexample, the femur and tibia will tend to be subjected to compressiveforces, while the humerus, radius and ulna will tend to be subjected totension.

SUMMARY OF THE INVENTION

The present invention addresses the need for intercalary prostheticsthat can be used to replace portions of the diaphyseal parts of the longbone that have been removed or excised. The present invention addressesthis need while also addressing the need for such prosthetics that canbe implanted and affixed to the remaining parts of the native bone whileminimizing damage to soft tissue at the ends of the native bone.

In one aspect, the present invention provides an intercalary implant foruse in replacing a missing portion of the shaft of a long bone, whereinthe long bone includes native proximal and distal portions havingintramedullary canals. The implant comprises a first stem member, asecond stem member and a collar. The first stem member includes a stemportion to be received in the intramedullary canal of one of the nativeportions of the long bone and a threaded male portion to be positionedoutside of the intramedullary canal. The second stem member includes astem portion to be received in the intramedullary canal of the other ofthe native portions of the long bone. The second stem member furtherincludes a spacer portion to be positioned outside of the intramedullarycanal and a shoulder to be positioned outside of the intramedullarycanal. The spacer portion is between the stem portion and the shoulder.The collar includes an annular base portion with an opening and acylindrical portion open at one end. The cylindrical portion has athreaded interior surface to receive and mate with the threaded maleportion of the first stem member. The collar receives part of the secondstem member through the opening in the base portion of the collar, andthe collar is movable in a proximal-distal direction along at least partof the length of the spacer portion of the second stem member between anextended position and a retracted position. In the extended position theannular base portion of the collar is spaced from the stem portion ofthe second stem member and abuts the shoulder of the second stem memberand the cylindrical portion of the collar extends over and beyond theshoulder of the second stem member. In the retracted position the collaris positioned so that at least part of the shoulder is exposed. Theshoulder and the opening of the annular base portion of the collar aresized and shaped so that when the collar is threaded onto the threadedmale portion of the first stem member the position of the first stemmember is fixed with respect to the position of the second stem member.

In another aspect, the present invention provides a surgical kit for usein treating a long bone of a patient wherein a portion of the shaft ofthe long bone is missing or resected and native proximal and distalportions of the long bone remain. The kit comprises a first stem member,a second stem member and a collar. The first stem member includes a stemportion and a threaded male portion. The second stem member has anoverall axial dimension and includes a stem portion, a spacer portionhaving an axial dimension and a radial dimension, and a shoulder havingan axial dimension and a radial dimension. The spacer portion is betweenthe stem portion and the shoulder. The radial dimension of the shoulderis greater than the radial dimension of the spacer portion. The collarmember includes an annular base portion with an opening and acylindrical portion open at one end. The collar member has a threadedinterior surface to receive and mate with the threaded male portion ofthe first stem member. The cylindrical portion has an interior radialdimension and an axial dimension. The annular base portion has a radialdimension and the opening of the annular base portion has a radialdimension. The radial dimension of the shoulder of the second stemmember is greater than the radial dimension of the opening in theannular base portion of the collar. The interior radial dimension of thecylindrical portion of the collar is greater than the radial dimensionof the spacer of the second stem member and the radial dimension of theshoulder of the second stem member. The axial dimension of thecylindrical portion of the collar is greater than the axial dimension ofthe shoulder of the second stem member.

In another aspect, the present invention provides a method of surgicallyreplacing a missing part of the shaft of a long bone. The methodcomprises preparing the long bone so that proximal and distal portionsof the long bone remain. The proximal and distal portions of the longbone each having an intramedullary canal. An intercalary implant isprovided. The intercalary implant has a first stem member, a second stemmember and a collar. The first stem member includes a stem portion and amale threaded portion. The second stem member includes a stem portion, aspacer and a shoulder. The collar includes a female threaded portion.The stem portion of one of the stem members is implanted in theintramedullary canal of the proximal portion of the long bone. The stemportion of the other of the stem members is implanted in theintramedullary canal of the distal portion of the long bone. The maleportion of the first stem member is positioned against the shoulder ofthe second stem member without distracting the proximal and distal partsof the bone in the proximal-distal direction. The collar is threadedonto the threaded male portion of the second stem member withoutdistracting the proximal and distal parts of the bone in theproximal-distal direction to assemble the intercalary implant.

In another aspect, the present invention provides, in combination, aproximal portion of a long bone, a distal portion of the long bone andan intercalary implant. The proximal portion has an intramedullary canaland a resected end surface. The distal portion has an intramedullarycanal and a resected end surface. The two resected end surfaces arespaced from each other. The intercalary implant comprises a first stemmember, a second stem member and a collar. The first stem member has astem portion received in the intramedullary canal of one of the portionsof the long bone. The second stem member has a stem portion received inthe intramedullary canal of the other portion of the long bone. One ofthe stem members also has a male threaded member. The collar has afemale threaded portion engaging the male threaded member. The otherstem member has a spacer and a shoulder connected to its stem portion.At least a portion of the collar bears against a portion of theshoulder. The distance between the resected end surfaces of the boneportions is fixed by the intercalary implant.

Additional features of the present invention will become apparent tothose skilled in the art upon consideration of the following detaileddescription of preferred embodiments exemplifying the best mode ofcarrying out the invention as presently perceived.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a top plan or anterior view of a humerus, showing the nativeproximal and distal ends of the humerus and showing an excisedintercalary segment of the diaphysis of the humerus in phantom betweenthe native ends of the humerus;

FIG. 2 is a top plan or anterior view of the humerus of FIG. 1, shownwith one type of intercalary prosthesis prior to assembly of all theparts of the intercalary prosthesis;

FIG. 3 is a top plan or anterior view of the humerus of FIGS. 1-2, shownwith all parts of the intercalary prosthesis assembled together;

FIG. 4 is an elevation of an exemplary first stem member component ofthe intercalary implant of the present invention;

FIG. 5 is an elevation of an exemplary second stem member component ofthe intercalary implant of the present invention;

FIG. 6 is an end view of the stem member component of FIG. 4, taken fromthe perspective of line 6-6 of FIG. 4;

FIG. 7 is an end view of the stem member component of FIG. 5, taken fromthe perspective of line 7-7 of FIG. 5;

FIG. 8 is an elevation of an exemplary collar component of theintercalary implant of the present invention;

FIG. 9 is an end view of the collar component of FIG. 8, taken from theperspective of line 9-9 of FIG. 8;

FIG. 10 is an opposite end view of the collar component of FIGS. 8-9,taken from the perspective of line 10-10 of FIG. 8;

FIG. 11 is a cross-section of the collar component of FIGS. 8-10, takenalong line 11-11 of FIG. 9;

FIG. 12 is a perspective view of the collar component of FIGS. 8-11;

FIG. 13 is an elevation of a kit including first, second and third stemmembers and a collar component;

FIG. 14 is an elevation of an exemplary embodiment of an intercalaryimplant assembled from the components of FIGS. 4-12;

FIG. 15 is an elevation of an exemplary embodiment of an assembledintercalary implant for use in spanning a longer gap in a bone;

FIG. 16 is a perspective view of the assembled intercalary implant ofFIG. 14;

FIG. 17 is a perspective view of the assembled intercalary implant ofFIG. 15;

FIG. 18 is an end view of the assembled intercalary implant of FIG. 14,taken from the perspective of line 18-18 of FIG. 14;

FIG. 19 is an end view of the assembled intercalary implant of FIG. 14,taken from the perspective of line 19-19 of FIG. 14;

FIG. 20 is a top plan or anterior view of two end portions of a humeruswith a gap illustrating where part of the bone shaft has been removed;

FIG. 21 is a top plan or anterior view of the two end portions of thehumerus of FIG. 20 shown with two stem portions of the present inventionimplanted, prior to the final assembly of the intercalary implant; and

FIG. 22 is a top plan or anterior view of two end portions of a humeruswith the assembled intercalary implant of the present inventionimplanted.

DETAILED DESCRIPTION

FIG. 1 illustrates a long bone, and in particular, a humerus 10 withproximal and distal ends 12, 14. The proximal end 12 of the humerus 10comprises the head and adjacent bone tissue; the distal end 14 of thehumerus comprises the trochlea and adjacent bone tissue. FIG. 1 alsoillustrates in phantom the intercalary segment 16 of diaphyseal bonethat has been removed, due to, for example, disease or severe trauma.Although the present invention is illustrated in use with the humerus,it should be understood that the invention is not so limited; theinvention could be used in any other long bone, such as the tibia orfemur, where a portion of the shaft has been removed or is missing.

FIG. 2 illustrates the humerus 10 of FIG. 1 in an intra-operative state,with a modular mid-shaft prosthesis 18. FIG. 3 illustrates the humerus10 of FIGS. 1-2 at the end of the surgical procedure. The mid-shaftprosthesis 18 of FIG. 2 is like that disclosed in U.S. patentapplication Ser. No. 10/135,791 filed on Apr. 30, 2002 and entitled“Modular Limb Preservation System,” and is shown at FIGS. 5 and 9 ofthat patent application. That patent application is incorporated byreference herein in its entirety.

The mid-shaft prosthesis 18 illustrated in FIGS. 2-3 comprises aproximal stem component 20, a distal stem component 22 and a spacercomponent 24. Each of the stem components 20, 22 includes a head portion26 from which extends a male connection element Morse taper post 28. Thehead portion 26 also includes a pair of notches that receive tabs on thespacer component 24. Each of the stem components 20, 22 also includes astem portion 30 that is shaped to be received in the intramedullarycanal of the bone.

As shown in FIG. 2, to implant the mid-shaft prosthesis 18 in the bone10, the two stem components 20, 22 may be implanted in theintramedullary canals of the two spaced ends 12, 14 of the bone 10. Thespacer component 24 can be connected to one of the stem portions 20, 22before the stem portion is implanted, or could also be connected afterthe stem portion is implanted. To complete the assembly, the nativeproximal and distal ends 12, 14 of the bone 10 with the proximal anddistal stem components 20, 22 and spacer component 24 must bedistracted, or moved in the proximal-distal direction, by at least adistance “d” (shown in FIG. 2), corresponding with the length of theMorse taper post 28 so that the Morse taper post 28 can be inserted intothe mating female portion of the spacer component 24. In the illustratedembodiment, the dimension “d” is typically on the order of 20 mm. Thisdegree of proximal-distal distraction of the native bone ends 12, 14could damage the surrounding soft tissue and soft tissue that isconnected to the native bone ends 12, 14.

To avert the potential for soft tissue damage, the present inventionobviates the need for proximal-distal distraction of the native boneends 12, 14. In the present invention, first and second stem members 40,42, shown in FIGS. 4-5, can be connected to each other without unduedistraction of the native proximal and distal end bone portions 12, 14.

The first and second stem members 40, 42 of the present invention can beconnected by means of a collar 44, shown in FIGS. 8-12, to form anassembly that defines the mid-shaft or intercalary implant of thepresent invention shown at 46 in FIGS. 14, 16 and 22. The mid-shaft orintercalary implant 46 comprises first and second stem members orcomponents. A surgical kit including the intercalary prosthesis 46 ofthe present invention could include one or more stem members of adifferent overall axial length, shown at 42A in FIGS. 15 and 17, and asan assembly at 46A in FIGS. 15 and 17. All of the components 40, 42, 44can be made of standard medical grade material for implants, such asstandard titanium alloys and cobalt-chrome alloys.

As shown in FIG. 4, the first stem member 40 includes a stem portion 48and a threaded male portion 50. In the illustrated embodiment, thethreaded male portion 50 and stem portion 48 are integral, although itshould be understood that the invention is not limited to an integralstructure unless expressly called for in the claims. The stem portion 48of the first stem member 40 may have features that allow it to be eithercemented or press fit into the intramedullary canal (shown at 52 in FIG.20) of the end portion of the native bone; for example, part or all ofthe stem portion can have a porous surface. It should be understood thatalthough FIGS. 21-22 illustrate the first stem member 40 being implantedin a distal end portion 14 of the humerus 10, the first stem member 40could be implanted in the proximal end portion 12 of the humerus 10 orproximal or distal end portion of another long bone such as the tibia,femur or radius or ulna.

A surgical kit utilizing the principles of the present invention couldinclude several sizes and types of first stem members 40 with threadedmale portions 50; for example, such stem members could be provided withstem portions of different lengths, some of which could have poroussurfaces. Generally, at least a set of the first stem members 40 of thesurgical kit would include threaded male portions 50 having similarcharacteristics such as size and thread characteristics, so that all ofthe first stem members 40 of the set would be interchangeable.Additional sets of first stem members with different sizes of malethreaded portions could be included to accommodate different diametersof bone.

The first stem member 40 also includes a stop member 53 defining anenlarged diameter shoulder 54 at the junction of the stem portion 48 andthe threaded male portion 50. The enlarged diameter shoulder 54 has aradial dimension shown at “r₁” FIG. 6 and an axial dimension shown at“a₁” in FIG. 4.

As shown in FIG. 5, the second stem member 42 or component includes astem portion 56, a spacer portion 58 and a shoulder 60. The end of thesecond stem member 42 opposite the stem portion 56 comprises a solidcylindrical disc or stop member as shown at 62 in FIG. 7, and having aradial dimension “r₂”. The annular surface of the stop member 62adjacent the spacer 58 defines the shoulder 60. In the illustratedembodiment, the stem portion 56, spacer portion 58 and stop member 62are integral, although it should be understood that the invention is notlimited to an integral structure unless expressly called for in theclaims. The stem portion 56 of the second stem member 52 may havefeatures that allow it to be either cemented or press fit into theintramedullary canal 52 of the end portion of the native bone; forexample, part or all of the stem portion have a porous surface. Itshould be understood that although FIGS. 21-22 illustrate the secondstem member 42 being implanted in a proximal end portion 12 of thehumerus 10, the second stem member 42 could be implanted in the distalend portion 14 of the humerus 10 or proximal or distal end portion ofanother long bone such as the tibia, femur or radius or ulna.

As shown in FIG. 5, the spacer portion 58 of the second stem member 42is adjacent the stem portion 56, and is between the stem portion 56 andthe shoulder 60 of the stop member 62. In the illustrated embodiment,the spacer portion 58 is generally cylindrical in shape, and has aradial dimension shown at “r₃” in FIG. 5. The radial dimension r₃ of thespacer portion 58 is greater than the greatest thickness of the stemportion 56 . The radial dimension r₃ of the spacer portion 58 is largeenough so that when the stem portion 56 of the second stem member 42 isimplanted in the intramedullary canal 52 of the end bone portion 12, thespacer portion 58 is retained outside of the bone, occupying part of thespace left by the removed bone shaft, as shown in FIGS. 21-22.

The axial dimension of the spacer portion, shown at “a₂” in FIG. 5, islarge enough so that, when combined with the axial dimension of the stopmember 62 and axial dimension a₁ of the male threaded portion 50, thetotal length is great enough to span the gap (shown at 64 in FIG. 20)left by the removed bone shaft.

A surgical kit utilizing the principles of the present invention couldinclude several sizes and types of stem members with spacer portions 58and shoulders 60; for example, such stem members could be provided withstem portions 56 of different lengths, some of which could have poroussurfaces. As illustrated in FIGS. 14-17, the axial length a₂ of thespacer portion 58 could be varied, such as by increasing the length. Asurgical kit utilizing the principles of the present invention couldinclude a third, fourth or more stem members similar to the illustratedsecond stem member 42, but with spacer portions 58 of graduallyincreasing axial lengths a₂ to provide the surgeon with a kit that canbe used to span mid-shaft gaps 64 of various lengths. For example, a kitcould include multiple stem members like those shown at 42, where theaxial length a, could increase in 5 mm increments. All of these stemmembers could be made to be used interchangeably with the collar 44 andfirst stem member 40. It should be understood that the present inventionis not limited to provision of such a kit or to any particularincremental increase in axial length unless expressly called for in theclaims. A kit including two stem members with different sizes of spacers58, 58A is illustrated in FIG. 13 at 65.

The radial dimension r₂ of the shoulder 60 is greater than the radialdimension r₃ of the spacer 58 of the second stem member 42. Although inthe illustrated embodiment the shoulder 60 is annular in shape, othershapes may be used so long as the shoulder 60 serves as a stop to limitmovement of the movable collar 44.

It should be understood that “radial dimension” as used throughout thisspecification and claims should not be interpreted as requiring anyparticular shape of any portion of the first and second stem members orcollar; “radial dimension” should be interpreted as including a width ofthe relevant portion of the stem members.

An example of a suitable collar member 44 is illustrated in FIGS. 8-12.As there shown, the collar 44 includes an annular base portion 70 and ahollow cylindrical portion 72. In the illustrated embodiment, theannular base portion 70 and the cylindrical portion 72 are integral,although it should be understood that the present invention is notlimited to such an integral structure unless expressly called for in theclaims.

The annular base portion 70 of the collar 44 has an overall radialdimension shown at “r₄” in FIG. 11 and a central opening 74 with areduced radial dimension shown at “r₅” in FIGS. 9 and 11. The centralopening 74 is large enough so that the collar 44 can be mounted on thesecond stem member 42 by inserting the free end of the stem portion 56through the central opening 74 and sliding the collar 44 up along thelength of the stem portion 56 and along the length of the spacer 58until the annular base portion 70 of the collar 44 abuts the shoulder60. The radial dimension r₅ of the central opening 74 is greater thanthe largest radial dimension r₃ of the spacer 58 and greater than thelargest radial dimension r₆ of the stem portion 56. The radial dimensionr₅ of the central opening 74 should be less than the radial dimension r₂of the shoulder 60 so that the shoulder 60 can serve as a stop to limitaxial movement of the collar 44 in the direction of the first stemmember 40.

The hollow cylindrical portion 72 of the collar 44 is threaded to matewith the threaded male portion 50 of the first stem member 40. Thecylindrical portion 72 of the collar 44 is open opposite the base 70 toreceive the threaded male portion 50 of the first stem member 40. Thecylindrical portion 72 of the collar 44 has an interior radial dimensionr₇ (shown in FIG. 10) and an axial dimension a₃ (shown in FIG. 11). Theinterior radial dimension of the cylindrical portion is greater than theradial dimension of the spacer 58 and greater than the radial dimensionof the shoulder 60.

In the illustrated embodiment, the mating threaded parts, that is, themale threaded portion 50 of the first stem member 40 and the collar 44,have a locking threaded relationship. One way of producing such alocking threaded relationship is to form a wedge ramp in the threads ofthe female collar 44 using equipment available from SpiralockCorporation, a Detroit Tool Industries Company, of Madison Heights,Mich. A locking threaded relationship is valuable in limiting possibleloosening of the threaded connection through vibration or use. It shouldbe understood that use of a wedge ramp and use of Spiralock Corporationequipment are identified as examples only; the present invention is notlimited to the use of locking threads or any particular types of lockingthreads unless expressly called for in the claims.

The collar 44 has an extended position and a retracted position on thesecond stem member 42. In the extended position shown in FIGS. 14-17 and22, the annular base portion 70 of the collar 44 is spaced from the stemportion 56 of the second stem member 42 and abuts the shoulder 60 of thesecond stem member 42. In this extended position, the cylindricalportion 72 of the collar 44 extends over and beyond the shoulder 60 andstop member 62 of the second stem member 42. The extended position ofthe collar 44 is at the end of its possible range of motion along thesecond stem member 42. The collar 44 is movable along the stem member 42away from the extended position to several possible retracted positions.In at least one of the retracted positions, shown in FIG. 13, at leastthe shoulder 60 of the second stem member 42 is exposed beyond thecollar 44. Another retracted position is illustrated in FIG. 21; asshown in FIG. 21, the end surface of the stop member 62 that defines theshoulder 60 is exposed.

The present invention also provides a method of replacing a missing partof the shaft of a long bone, such as part 64 of bone 10. The long bone10 is prepared so that proximal and distal portions 12, 14 of the longbone remain. The distal end of the proximal portion 12 and proximal endof the distal portion 14 can be resected in a standard manner and cut orplaned to define flat planar surfaces. The intramedullary canals 52 ofthe proximal and distal portions 12, 14 of the long bone 10 can bereamed in a standard manner to prepare the bone portions 12, 14 toreceive the implant 46.

Suitable trials duplicating the span that will be provided by theintercalary implant 46 can be used prior to implantation to ensure thatthe length of the intercalary implant 46 will be appropriate.

One of the stem portions of one of the stem members is implanted in theintramedullary canal of the proximal portion of the bone and the stemportion of the other stem member is implanted in the intramedullarycanal of the distal portion of the bone. In the embodiment illustratedin FIGS. 21-22, the first stem member 40 is implanted in the distal endportion 14 of the bone 10 and the second stem member 42 is implanted inthe proximal end portion 12 of the bone 10. It should be understood thatthe first stem member 40 could be affixed to either the proximal portion12 or the distal portion 14 of the bone 10, and the second stem member42 could be affixed to either the proximal portion 12 or distal portion14 of the bone 10.

It should be understood that the present invention could involve use ofstem members 40, 42 with stem portions 56 designed to be cemented inplace in the intramedullary canal or stem members with stem portionsdesigned to be interference fit in the intramedullary canal. Thesurgical method used will include appropriate steps to accommodate thedesign selected for the particular patient.

When implanted, the shoulder 54, stop member 53 and male threadedportion 50 of the first stem member 40 are exposed beyond the endsurface of the bone end; the remainder of the first stem member 40 isreceived in the bone end. When implanted, the spacer 58 and disc or stopmember 62 of the second stem member 42 are exposed beyond the endsurface of the bone end. The entire collar 44 is also exposed outside ofthe bone.

After the two stem portions 40, 42 have been implanted, assembly of theintercalary implant 46 may then be completed. As shown in FIG. 21, theouter edge of the male threaded portion 50 of the first stem member 40is positioned against the outer surface of the stop member 62 of thesecond stem member 42. The two stem members 40, 42 can be so positionedwithout distracting the proximal and distal portions 12, 14 of the bonein the proximal-distal direction. The collar 44 is then moved axiallyalong the spacer 58 and threaded onto the male portion 50 of the firststem member 40; the collar 44 is tightened on the threaded male portion50 of the first stem member 40 until the base 70 of the collar abuts theshoulder 60 of the second stem member 42 and the outer edge of thecollar 44 abuts the outer surface of the shoulder 54 of the stop member53 of the first stem member 40. The two stem members 40, 42 and thecollar 44 are thereby securely assembled together without anydistraction of the proximal and distal portions 12,14 of the bone 10 inthe proximal-distal direction. Thus, potential damage to the soft tissueat the ends of the bone 10 is eliminated or at least substantiallyreduced.

An assembly of the components 40, 42, 44 of the intercalary implant isillustrated in FIG. 22 with respect to the humerus, and shown withoutbeing implanted in FIGS. 14-17. When assembled, the free end of the maleportion 50 of the first stem member 40 abuts the outer surface 63 of thestop member 62 of the second stem member 42. The opposite shoulder 60 ofthe stop member 62 of the second stem member 42 abuts the inner surfaceof the annular base 70 of the collar 44. The threaded cylindricalportion 72 of the collar 44 extends over and engages the threaded maleportion 50 of the first stem member 40. The outer edge of the threadedcylindrical portion 72 abuts the shoulder 54 of the stop member 53 ofthe first stem member 40. Thus, when assembled, the overall length ofthe intercalary implant 46 is fixed, and the overall length of the partof the intercalary implant spanning the gap left in the bone shaft isfixed as the total of the axial dimensions of the spacer 58 of thesecond stem member 42, collar 44 and stop member 53 of the first stemmember 40. It should be understood that the overall length of the partof the intercalary implant spanning the gap left in the bone shaft couldalso include a part of the male threaded portion 50 of the first stemmember 40 if for some reason the collar 44 is not tightened until itabuts the shoulder 54 of the first stem member 40.

It should be understood that the above-described surgical technique isprovided by way of example only, and that the present invention is notlimited to that technique unless expressly called for in the claims.

An alternative intercalary prosthesis, kit and method is disclosed in anapplication for U.S. patent filed concurrently herewith by Stephen A.Hazebrouck and entitled “Intercalary Prosthesis, Kit and Method,” whichis incorporated by reference herein in its entirety.

While only specific embodiments of the invention have been described andshown, it is apparent that various alternatives and modifications can bemade thereto. Those skilled in the art will also recognize that certainadditions can be made to the illustrative embodiments. For example, aspacer element could also or alternatively be provided on the first stemmember 40 between the threaded male portion 50 and the stem portion 48.It is, therefore, the intention in the appended claims to cover all suchalternatives, modifications and additions as may fall within the truescope of the invention.

1. An intercalary implant for use in replacing a missing portion of theshaft of a long bone, wherein the long bone includes native proximal anddistal portions having intramedullary canals, the implant comprising: afirst stem member including a stem portion to be received in theintramedullary canal of one of the native portions of the long bone, thefirst stem member including a threaded male portion to be positionedoutside of the intramedullary canal; a second stem member including astem portion to be received in the intramedullary canal of the other ofthe native portions of the long bone, the second stem member furtherincluding a spacer portion to be positioned outside of theintramedullary canal and a shoulder to be positioned outside of theintramedullary canal, the spacer portion being between the stem portionand the shoulder; and a collar including an annular base portion with anopening and a cylindrical portion open at one end, the cylindricalportion having a threaded interior surface to receive and mate with thethreaded male portion of the first stem member; wherein: the collarreceives part of the second stem member through the opening in the baseportion of the collar, and the collar is movable in a proximal-distaldirection along at least part of the length of the spacer portion of thesecond stem member between an extended position and a retractedposition; in the extended position the annular base portion of thecollar is spaced from the stem portion of the second stem member andabuts the shoulder of the second stem member and the cylindrical portionof the collar extends over and beyond the shoulder of the second stemmember; in the retracted position the collar is positioned so that atleast part of the shoulder is exposed; and the shoulder and the openingof the annular base portion of the collar are sized and shaped so thatwhen the collar is threaded onto the threaded male portion of the firststem member the position of the first stem member is fixed with respectto the position of the second stem member; the shoulder of the secondstem member has a radial dimension and an axial dimension; the openingin the annular base portion of the collar has a radial dimension; thespacer of the second stem member has a radial dimension and an axialdimension; the cylindrical portion of the collar has an interior radialdimension and an axial dimension; the radial dimension of the shoulderof the second stem member is greater than the radial dimension of theopening in the annular base portion of the collar; the interior radialdimension of the cylindrical portion of the collar is greater than theradial dimension of the spacer of the second stem member; the interiorradial dimension of the cylindrical portion of the collar is greaterthan the radial dimension of the shoulder of the second stem member; andthe axial dimension of the cylindrical portion of the collar is greaterthan the axial dimension of the shoulder of the second stem member.
 2. Amethod of surgically replacing a missing part of the shaft of a longbone comprising: preparing the long bone so that proximal and distalportions of the long bone remain, the proximal and distal portions ofthe long bone each having an intramedullary canal; providing a firststem member, a second stem member and a collar, wherein the first stemmember includes a stem portion and an integral male threaded portion,the second stem member includes a stem portion, an integral spacer andan integral shoulder, and the collar includes a female threaded portion;implanting the stem portion of one of the stem members in theintramedullary canal of the proximal portion of the long bone;implanting the stem portion of the other of the stem members in theintramedullary canal of the distal portion of the long bone; positioningthe male portion of the first stem member against the shoulder of thesecond stem member without distracting the proximal and distal parts ofthe bone in the proximal-distal direction; and assembling the first stemmember, second stem member and collar by threading the collar onto thethreaded male portion of the second stem member without distracting theproximal and distal parts of the bone in the proximal-distal directionwithout inserting any portion of the first stem member into any portionof the second stem member and without inserting any portion of thesecond stem member into any portion of the first stem member.